Measurement of absolute E2 transition strengths in {sup 176}W: Signatures for a rapid shape change
The X(5) symmetry describes nuclei at the critical point of the shape phase transition from axially deformed rotor nuclei to spherical vibrators. {sup 150}Nd, {sup 152}Sm, and {sup 154}Gd were the first nuclei where the predicted characteristics of the X(5) symmetry were observed. Later it was shown that also {sup 176,178,180}Os can be successfully described with the X(5) symmetry.In the close vicinity of shape phase transitions one expects strongly changing nuclear shapes. In the X(5) region around A = 150 this was observed for nuclei with different neutron numbers, whereas in the X(5) region around A = 180 this is to be expected for different proton numbers. The aim of the work presented here is the confirmation of a rapid shape change for nuclei close to {sup 178}Os. Besides the knowledge on the level scheme of the nuclei of interest, especially absolute E2 transition strengths are crucial for the interpretation of nuclear structure. Prolate deformation is expected for {sup 176}W. Thus we performed a recoil distance Doppler shift (RDDS) measurement on {sup 176}W to measure E2 transition strengths from level lifetimes. The experiment was performed at the Cologne FN TANDEM accelerator with the Cologne coincidence plunger with the reaction {sup 169}Dy({sup 16}O,4n){sup 176}W and a beam energy of 80 MeV. We will present our experimental results and relate them to data on the neighboring nuclei {sup 178}Os and {sup 182}Pt. The results will be discussed in the framework of nuclear shape transitions in this mass region and compared to calculations with both the Interacting Boson Model (IBM) and the GCM.